1. Field of the Invention
The present invention relates generally to probes for probe cards and more particularly, to a spring probe.
2. Description of the Related Art
Upon testing semiconductor chips, a tester is electrically connected with devices under test (hereinafter referred to as the “DUTs”) through a probe card, so that the tester can obtain the testing results of the DUTs by means of signal transmission and analysis. The conventional probe card is usually composed of a circuit board and a probe device, or further comprises a space transformer disposed between the circuit board and the probe device. The probe device has a plurality of probes arranged corresponding to contact pads of the DUTs, so that the contact pads can be probed by the probes at the same time.
FIG. 1 is an exploded plan view of a conventional spring probe 11 which comprises a needle 12, and a spring sleeve 13 sleeved onto the needle 12. FIG. 2 is a schematic sectional view of a probe card 14 using the spring probe 11. For the convenience of illustration, FIG. 2 is not drawn to the same scale with FIG. 1. The probe card 14 comprises a circuit board 15 and a probe device 16 having a probe seat 17 and a plurality of probes 11. For the convenience of illustration, only a small part of the circuit board 15 and the probe seat 17 and one of the probes 11 are shown in FIG. 2.
The needle 12 and the spring sleeve 13 of the probe 11 are connected in a way that a connection section 132, which is provided near the bottom end of the spring sleeve 13, is pressed against the needle 12 and fixed to the needle 12 by welding, such as spot welding. The probe seat 17 is composed of upper, middle and lower dies 171, 172, 173; however, the probe seat 17 may be provided without such middle die 172 but composed of the upper and lower dies 171, 173 only. The probe seat 17 has a plurality of installing holes 174 provided in the assembly of the dies 171, 172, 173 (only one of the installing holes 174 is shown in FIG. 2). Each installing hole 174 is composed of an upper guiding hole 171a of the upper die 171, a middle guiding hole 172a of the middle die 172, and a lower guiding hole 173a of the lower die 173, and adapted for accommodating therein a probe 11. The probe 11 is installed in the probe seat 17 in a way that the connection section 132 of the spring sleeve 13 is orientated toward the upper die 171, and thereafter passes through the upper guiding hole 171a and the middle guiding hole 172a in order, and then the connection section 132 is eventually located in the lower guiding hole 173a of the lower die 173 in a way that a bottom section of the needle 12 is inserted through a through hole 173b of the lower die 173 and protrudes out of the lower die 173. By this way, a bottom surface of the connection section 132 of the probe 11 is supported on a bottom surface of the lower guiding hole 173a of the lower die 173. As a result, the probe 11 is kept in the upper, middle and lower dies 171, 172, 173 and prevented from escape from the probe seat 17.
After the probe device 16 is assembled completely, the circuit board 15 is disposed on the top surface 175 of the probe seat 17. The top end of the spring sleeve 13 is electrically connected with a contact pad of the circuit board 15. The bottom end of the needle 12 is adapted to probe a contact pad of the DUT. Specifically speaking, the top end of the spring sleeve 13 is abutted against the circuit board 15, and the spring sleeve 13 is provided with two spring sections 138 which are compressible elastically; besides, the connection section 132 of the spring sleeve 13 is fixed to the bottom section of the needle 12, and a clearance 18 is provided between the top end of the needle 12 and the circuit board 15, i.e. between the top end of the needle 12 and the top end of the spring sleeve 13. Therefore, when the bottom end of the needle 12 contacts the contact pad of the DUT and correspondingly feeds forward, the needle 12 will retract backward, such that the sleeve 13 will be compressed. In this way, the probe 11 can positively contact and electrically connect the contact pad of the DUT; besides, by means of the cushioning effect provided by the spring sleeve 13, an exceeding contact force, which may cause damage or heavy wear of the contact pad of the DUT or the needle, can be prevented.
When the circuit board 15 is electrically connected with a tester (not shown) and the contact pad of the DUT is probed by the bottom end of the needle 12, testing signals can be transmitted between the tester and the DUT through the spring sleeve 13 and the needle 12. Specifically speaking, it is optimal that the needle 12, rather than the spring sleeve 13, is the primary element of the probe 11 used for transmitting the testing signals, and the tail 122 of the needle 12 shall be in contact with the non-spring section 139 provided at the top of the spring sleeve 13, so that the signal transmission between the needle 12 and the spring sleeve 13 occurs at the non-spring section 139. For example, after the signal is transmitted from the DUT to the bottom end of the needle 12, it is optimal that the signal is transmitted to the tail 122 of the needle 12 through the body of the needle 12 itself and then transmitted to the circuit board 15 through the non-spring section 139 at the top of the spring sleeve 13.
However, it is not ensured that the tail 122 of the needle 12 of the conventional spring probe 11 can be in contact with the non-spring section 139 at the top of the spring sleeve 13. Therefore, the testing signals are likely transmitted between the connection section 132 and the needle 12 and transmitted through the spring sections 138, resulting in unstable signal transmission. Besides, because the spring sections 138 have small cross section area, they are unable to bear large electric current. Therefore, the spring sections 138 tend to fracture due to overload of electric current when signals are transmitted therethrough. In addition, because the spring sections 138 have relatively longer path for signal transmission, the spring sections 138 may have great inductance, such that the transmitting bandwidth of the signals passing through the spring sections can hardly be improved. As a result, the conventional spring probe 11 is unsuitable for high frequency testing.